I recently purchased a Steam Deck, which uses KDE Plasma as its desktop. I'm looking for a way to draw on the desktop with the device's touchscreen, and found some sites suggesting the built in Mouse Mark mode, but that appears to rely on keyboard shortcuts to activate it.

Is there any way to activate this feature without a physical keyboard connected? If not, is there a similar feature available for tablet devices like this?

Hi,
The mouse mark cannot be configured to do what you need from the GUI, but it most likely can be if one is familiar with the command line and scripting. Unfortunately, I don't know how to that; but I just wanted to suggest an app I've used called Openboard. It has a mode which lets you draw on the desktop, but it actually shows a sidebar for the pen and eraser and other tools. So it's not exactly a replacement for the mouse mark option, but I thought it might cover your use case. BTW, it's available on Flathub, so it should be easy to install on the Deck.